The present invention relates generally to transducers, such as magnetostrictive position transducers for example, and, more specifically, to transducers which provide a pulsed output such that the time between pulses is proportional to the condition being measured and is compensated to account for various factors. In particular, in one embodiment, the present invention relates to a method and apparatus for generating magnetostrictive position transducer output pulses which are standardized for waveguide propagation speed (i.e., xe2x80x9cgradientxe2x80x9d), and which are also compensated to account for waveguide non-linearities.
A transducer may provide any of a variety of output signals. For example, an analog voltage (or current) output signal may be provided wherein the output voltage (or current) is directly proportional to the condition being measured. Alternatively, the transducer may provide a digital output, such as a synchronous serial interface (SSI) for example, in which the condition being measured is provided as a data word. The type of output which is provided by the transducer depends upon the particular environment in which the transducer will be used, and the controller or apparatus to which the output will be provided.
Another example of a transducer output is the start/stop output, or pulse interface, in which the time between a first and second pulse is directly proportional to the condition or quantity being measured. By way of example, in a magnetostrictive position transducer, a controller provides an interrogation pulse which results in an elastic deformation of a waveguide in the transducer originating at a magnetic marker on the transducer. The deformation propagates along the waveguide in both directions, in the form of a mechanical wave having longitudinal and torsional components. The mechanical wave is then converted to a response pulse by a suitable convertor, such as a coil, tape or crystal. The interrogation pulse and response pulse are provided as a start/stop pulse output, and the time between the two pulses represents the position of the magnet, which is connected to the movable mass being measured. The present invention is applicable to such pulsed output or pulse interface transducers, wherein the time between two pulses represents a condition or feature (e.g., a position) being measured.
The accuracy of transducers can be affected by imperfections and variances in the components and materials which make up the transducer. For example, the magnetostrictive waveguide of a position transducer can have variances in material and size across its length, which produce an undesirable non-linear output over the length of the waveguide. In other words, the transducer may not produce a perfectly linear output with respect to position along the waveguide, due to manufacturing variances along the waveguide. While careful screening of materials and components can reduce inaccuracies due to non-linearity, such screening and control can take time, can add to the expense of manufacturing the transducer, and can result in numerous waveguides which must be discarded.
Moreover, two transducers of the same type may produce differing outputs due to material variances or irregularities. As an example, due to slight differences in materials or structural variations, a magnetostrictive waveguide of one transducer may have a different propagation speed than that of another transducer. (The propagation speed or xe2x80x9cgradientxe2x80x9d of a waveguide is the speed at which a mechanical wave will travel along the waveguide.) Accordingly, such variances need to be taken into account in order for the output of the transducer to be accurately interpreted by the apparatus which receives the output of the transducer. For example, if a controller in a machine receives the pulsed output of a magnetostrictive position transducer, it conventionally needs to be programmed with the propagation speed of the transducer""s waveguide in order to accurately interpret the output of the transducer. Such programming requires the user to be experienced with the programming procedure, requires time on the part of the user in conducting the programming, and can be error-prone. Moreover, if the transducer must be replaced, the controller must be re-programmed to account for the particular characteristics of the replacement transducer. Also, such programming typically does not account for non-linearity.
Accordingly, it is desirable to allow for correction of imperfections and variances in a transducer, such as variances due to material composition and tolerances, without requiring input on the part of the user, without requiring programming for each particular transducer, and without requiring tedious and wasteful selection of materials or components. It is particularly desirable to provide such correction in the context of transducers which utilize magnetostrictive waveguides, where non-linearities and gradient variances can be problematic. Such compensation is particularly desired in applications where high accuracy is demanded.
In certain transducers, it has been known to provide some automatic compensation capabilities internally to the transducer, such that user input is not required. However, such compensation has heretofore not been provided in transducers which utilize a pulsed output. In particular, there has not been available a method or apparatus to accurately generate compensated output pulses from a transducer. For example, in the context of a magnetostrictive linear position transducer with a digital pulse interface, heretofore, no capability has been provided to change or re-create the pulsed output of the transducer.
Accordingly, there remains a need for a method and apparatus for changing or re-creating the output of a pulsed interface transducer so as to compensate for variances within a particular transducer (e.g., non-linearities) and/or variances between transducers (e.g., propagation speed differences), so as to eliminate calibration input from the user, and to avoid the need for careful screening and/or discarding of materials. Moreover, there remains a need for such a method and apparatus which can provide a highly accurate output with high resolution.
It is an object of the present invention to obviate the above-described problems.
It is a further object of the invention to provide a pulsed output transducer which does not require the user to calibrate the control system with which the transducer will be used.
It is yet another object of the invention to provide a method and apparatus to automatically compensate for non-linearities in a pulsed output transducer where the time between the output pulses represents the condition or feature being measured.
Yet another object of the invention is to provide a method and apparatus to automatically compensate for propagation speed variations in a pulsed output transducer.
Another object of the present invention is to provide a pulsed output transducer having compensated start and stop pulses with high output resolution, the time between the pulses representing the condition or feature being measured.
It is another object of the invention to provide a magnetostrictive linear position transducer having start/stop output pulses, which does not require the user to calibrate the control system with which the transducer will be used.
Another object of the invention to provide a magnetostrictive linear position transducer having start/stop output pulses which are compensated to account for variances due to non-linearities and/or propagation speed.
Yet another object of the invention is to provide a method and apparatus to generate automatically compensated start/stop output pulses from a magnetostrictive position transducer, the time between the pulses representing linear position with high accuracy.
It is another object of the invention is to provide a method and apparatus to generate start/stop output pulses from a magnetostrictive position transducer such that the time between the pulses represents predicted linear position and is automatically compensated for variances in the transducer.
Another object of the invention is to provide a linear position transducer which can be provided within a cylinder, while taking up less space and being more protected from damage.
To achieve the foregoing and other objectives, a method for providing a compensated linear position transducer output is provided. The method comprises generating an interrogation signal to create a mechanical wave in a waveguide, converting the mechanical wave to a response signal, measuring the time between the interrogation signal and the response signal, and calculating a position based upon the measured time. The method also comprises adjusting the calculated position such that it matches an ideal transducer having a linear waveguide response and a predetermined standard waveguide propagation velocity. In addition, the method comprises generating a start pulse and a stop pulse, the time between the pulses being derived from the adjusted position.
Also provided is a method for providing a compensated transducer output. The method comprises providing a digital value representing a detected condition, and adjusting the digital value to imitate the response of a predetermined ideal transducer. The method also comprises generating a first transducer output pulse, and generating a second transducer output pulse after the first pulse. The time delay between the first and second pulses is derived from the adjusted digital value.
A linear position transducer system is also provided comprising a waveguide, an interrogation pulse generator circuit, and a mode convertor in communication with the waveguide. The system also includes a calculation circuit in communication with the mode convertor and the interrogation pulse generator circuit. The calculation circuit is configured to measure the time between the generation of the interrogation signal from the interrogation pulse generator and the generation of a response signal from the mode convertor, and is also configured to generate a digital value based upon the time measurement. The system also includes a compensation circuit in communication with the calculation circuit. The compensation circuit is configured to adjust the digital value to create a compensated digital value which simulates the response of a waveguide having a predetermined standard propagation velocity. Also include in the system is a stop pulse generator circuit in communication with the compensation circuit and configured to generate a stop pulse based upon the compensated digital value.
In addition, a linear position transducer system is also provided comprising a cylinder, and a waveguide provided at least partially within the cylinder. The system also includes an interrogation pulse generator circuit, a mode convertor in communication with the waveguide, and a proximal electronics housing located adjacent the cylinder. Also included in the system is signal conditioning circuitry provided at least partially within the proximal electronics housing and in communication with the mode convertor. The signal conditioning circuitry is configured to convert an analog response pulse from the mode convertor to a digital pulse signal. Also included are remote electronics located remotely from the cylinder, comprising a calculation circuit in communication with the signal conditioning circuitry. The calculation circuit is configured to measure the time between the generation of an interrogation signal from the interrogation pulse generator and the generation of a digital pulse signal from the signal conditioning circuitry, and to generate a digital value based upon the measured time.
Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described preferred embodiments of this invention, including a best mode currently contemplated for carrying out the invention, simply for the purposes of illustration. As will be realized, the invention is capable of other different aspects and embodiments without departing from the scope of the invention. Accordingly, the drawings and descriptions are illustrative in nature and not restrictive in nature.